1. Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to an organic light emitting device and a driving method thereof.
2. Discussion of the Background
A hold-type flat panel display, such as an organic light emitting device, displays an image during a time period, for example, during a single frame, regardless of whether the image is a still image or motion image. For example, when an image of a continuously moving object is displayed, the movement of the object is discretely displayed such that the object stays at a particular position during one frame and then, during the next frame, the object stays at a position to which the object has moved after one frame. Because the afterimage is maintained during the time period of a frame, this method of display may effectively represent the continuous movement of the object.
However, the user's eyes continuously move on a screen along the movement of the object, and the continuous movement of the user's eyes conflicts with the discrete displaying scheme, which may cause blurring of an image. For example, it is assumed that a display device displays an image of the object such that the object stays at a position A during a first frame and the object stays at a position B during a second frame. During the first frame, the user's eyes move along an expected movement path of the object from position A to position B. In this respect, however, the object is not actually displayed at the intermediate positions between the positions A and B.
Consequently, the luminance recognized by the user during the first frame is equal to a value obtained by integrating the luminance of pixels in the path between the positions A and B, namely, a value obtained by appropriately averaging the luminance of the object and that of the background, which may cause the object to be blurred.
In the hold-type display device, since the degree of the blurring of the image of the object is proportional to a time period during which the display device maintains display of images, an impulse driving method has been proposed in which an image is displayed only for a limited portion of one frame and a black color is displayed for the remaining portion of the frame. In the impulse driving method, the luminance is reduced since the time period for actually displaying an image is reduced. Thus, a method for increasing the luminance during the display time and a method for displaying a median luminance with adjacent frames instead of a black color have been proposed. However, such methods may result in an increase in power consumption and a complicated driving scheme.
Each pixel in the organic light emitting device includes an organic light emitting element and a thin film transistor (TFT) to drive the organic light emitting element. When the light emitting elements and the TFTs operate for a long time, a threshold voltage thereof may change, thereby failing to provide an expected luminance. In addition, when the characteristics of semiconductors included in the TFTs are not uniform in the display device, luminance deviation among pixels may occur.